1. Field of the Invention
Optical pattern tracers are well known in the machine tool field and are commonly used to control the cutting of various machine tools, particularly gas and flame cutting machines which may be caused to cut specific shapes from material based upon a predetermined pattern. One class of such pattern tracers is optical pattern tracers which view a pattern, such as a dark silhouette or line on a white surface, and cause the tracer and its associated machine tool to follow the convolutions of the pattern. One of the preferred forms of optical tracers scans a circular area repetitively crossing the edge of the pattern and producing an electrical signal representative of the change of reflectance as the scanning action crosses the edge of the pattern. This electrical signal is then used, together with a reference signal and other information, to produce coordinate drive information to control X and Y drive motors which cause the machine to move with constant tangential velocity around the pattern.
With increasing sophistication of such equipment, the additional information which must be derived can produce quite complex electronic circuitry to enable the machine to identify not only the pattern itself but auxiliary marks associated with the pattern, sometimes called command marks, discontinuities in the pattern, and other conditions which give rise to special problems.
2. Description of the Related Art
Typical of the tracers of this class are those described in:
U.S. Pat. No. 3,704,372 issued Nov. 28, 1972 to Robert E. Parker, et al;
U.S. Pat. No. 3,727,120 issued April 10, 1973 to George S. Jewell, et al;
U.S. Pat. No. 3,860,862 issued Jan. 14, 1975 to William Dell, et al;
U.S. Pat. No. 3,883,735 issued May 13, 1975 to Francis P. Murphy, et al.